Today, digital media is commonly stored on floppy disks, hard disks and optical discs. The term “disk” or “disc” refers to a round plate onto which data can be digitally encoded and thereafter retrieved. Generally, there are two basic types of computer “disks”—magnetic and optical. Both “floppy disks” and “hard disks” refer to a magnetic-type disk whereas an optical disc usually refers to a reflective plastic disc.
Similar to cassette tapes, data can be recorded on and erased from any magnetic disk as many times as desired. To the contrary, most optical discs do not share the unlimited writable and/or rewritable characteristics of the magnetic medium. Rather, some optical discs are “read only” while others are “writable.” Still other optical discs are “re-writable” thereby enabling the disc to be erased and rewritten, much like a magnetic medium.
Generally, an optical disc refers to a data storage medium that includes data that can be read and/or written via lasers. Today, different types of lasers (e.g., red, blue) can be employed resulting in different storage capacity. This difference is largely owed to the wavelength associated with the laser type.
These reflective plastic platters or optical discs have become commonplace for the storage of text, audio, video as well as multi-media data. For example, the popularity of these plastic discs continues to increase in the personal computer as well as the consumer products markets. Nearly all PCs sold today are equipped with an optical drive or, alternatively, an optical drive can be added at a very nominal cost to the consumer. As well, optical discs are used commonly in other markets including, but not limited to, the music industry, the motion picture industry and the video gaming industry.
A CD-ROM (Compact Disc Read Only Memory) is a compact disc format commonly used to hold text, graphics and audio with respect to a PC. A common CD-ROM can house approximately 650 megabytes (MB) of data. This amount of data can be equated to about 250,000 pages of text or 20,000 medium-resolution images. Other CDs have become available that can house an increased amount of data.
Although similar in appearance to an audio CD, the format for recording data onto a CD-ROM is quite different. With respect to compatibility, a CD-ROM logical unit (e.g., drive) is compatible with an audio CD format and therefore can be used to play the music contained thereon. However, the converse is not true. A CD player cannot read or access data from a CD-ROM.
A CD-Recordable or CD-R is a recordable CD-ROM technology that uses a disc that can be written only a single time. Although these discs are restricted to a single write operation, they are oftentimes appendable. In other words, a user can add data to a CD-R but cannot write over existing data. As with all CDs, CD-Rs create the equivalent of pits in the disc by altering the reflectivity of a dye layer. Accordingly, a laser can be employed to read the reflectivity of the dye thereafter enabling obtaining information saved on the disc.
Because of their limited functionality and corresponding lower cost, CD-R discs are frequently used for original masters of CD-ROM material and for archiving data where re-writable functionality is not necessary. Today, to write or “burn” a complete 650 MB disc can take as little as five minutes compared to about an hour for older drives. This 650 MB capacity is equivalent to about 75 minutes of digital audio recording.
A CD-ReWritable or CD-RW refers to a rewritable CD-ROM technology. With respect to compatibility, a CD-RW drive can be used to write or burn CD-R discs. As well, a CD-RW drive can be employed to read CD-ROMs. However, because CD-RW disks have a lower reflectivity than CD-ROMs and CD-Rs, multiread CD-ROM drives are required to read them.
Unlike CD-Rs, in which the entire disc or an entire track is recorded at once, CD-RWs support Universal Disk Format (UDF), which can be equated to the file system on a hard disk. Using variable packet writing, small numbers of files can be appended, and using fixed packet writing, files can be added and deleted. The fixed packet approach requires pre-formatting like a floppy disk, but takes considerably longer.
A Digital Versatile Disc (DVD), formally Digital Video Disc, refers to a family of optical discs that share the same overall dimensions of a CD, but have significantly higher capacities. Additionally, where CDs are single-sided, DVDs may be double-sided. Recent developments have lead to dual-layer versions having two distinct layers of data per side. These discs are most often used in the music, motion picture and video gaming industries.
Similar to the CD-ROM, there are a number of varieties of DVDs. For example, a DVD-ROM can be described as a large CD-ROM that enables storage of a large amount of data, audio, video and interactive material. Similarly, for instance, a DVD±R and DVD±RW refer to the write-once and rewritable versions respectively.
A DVD±R or DVD Recordable refers to a write-once optical disk commonly used to master DVD-Video and DVD-ROM format discs. DVD±Rs are the DVD counterpart to CD-Rs and use the same dye-layer recording technology to “burn” the disc. A DVD Read Write or commonly known as a DVD±RW, refers to a type of rewritable DVD disk. Using phase change technology, the DVD±RW discs can retain up to 4.7 gigabytes (GB) per side and can be rewritten more than 1,000 times.
A DVD Video disc refers to a read-only DVD disc used for full-length movies. DVD-Video discs can hold approximately 133 minutes of full-motion video per side using MPEG-2 compression. Recent developments in technology have lead to high-definition television and subsequently, High Density Digital Versatile Discs or HD DVD.
HD-DVD refers to a digital optical media format which is being developed as one standard for high-definition DVD. With the increased popularity in high-definition television (HD TV) and transmission of HD programming, HD-DVD is increasing in demand. HD-DVD has a single layer capacity of 5 GB and a dual-layer capacity of 30 GB. Recently, other formats (e.g., Blu-Ray™) have emerged to compete with the HD-DVD standard. As such, developments have been focused upon increased storage capacity, decreased manufacturing cost and format compatibility in order to appeal to the marketplace.